1. Field of the Invention
The present invention relates to a control method for a claw-pole synchronous machine which is designed to be operated as a three-phase generator or a three-phase electric motor. More particularly, the present invention is concerned with a claw-pole synchronous machine controlling method which can ensure enhanced controllability of operation of the claw-pole synchronous machine without incurring any appreciable increase in the size and the cost involved in the implementation thereof.
2. Description of Related Art
In general, the internal combustion engine for a motor vehicle or the like is equipped with a three-phase synchronous machine operated as a generator or a motor. For driving such three-phase synchronous machine by using an inverter-type power supply source, a control method based on a combination of a vector control and a field current control is adopted and well known in the art, as is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 182380/19996 (JP-A-8-182380).
For better understanding of the concept underlying the present invention, background technique thereof will first be described in some detail.
FIG. 6 is a perspective view showing a rotor of a general claw-pole synchronous machine.
In FIG. 6, the rotor comprises a shaft 10, field poles (claw-poles) 11 and field coils 12, which are formed in one body. Fan blades 14 for cooling the field coils 12 are disposed on periphery of both end surfaces of the rotor respectively.
At first, let""s consider the case where the three-phase synchronous machine is operated as a motor (i.e., motor operation mode).
The torque Te generated by the three-phase synchronous machine in the motor operation mode is given by the following expression (1):
Te=3{xcexa8xc2x7iq+(Ldxe2x88x92Lq)idxc2x7iq}xe2x80x83xe2x80x83(1)
where xcexa8 represents total flux linkage determined by the field current if, Ld and Lq represent synchronous inductance transformed into d- and q-axis components, respectively, xcexa8xc2x7iq represents a torque generated by the flux linkage xcexa8, and the term (Ldxe2x88x92Lq)idxc2x7iq represents a reluctance torque, where id and iq represent armature phase currents, respectively, as elucidated below.
Further, the d-axis mentioned above represents the direct-axis direction which coincides with the field pole direction and the q-axis represents the quadrature-axis direction orthogonal to the field pole direction. In this connection, id and iq represent the armature phase currents for the vector control as transformed into the d- and q-axis components (direct- and quadrature-axis components), respectively. The armature phase currents id and iq bear the relation to the armature current i (phase current) which is given by the following expression (2).
i2=id2+iq2xe2x80x83xe2x80x83(2)
The armature current i is three-phase current. However, in the description which follows, it is assumed only for the convenience of description that the armature current i is two-phase current capable of generating a same electromotive force as the three-phase armature current i and represented by the phase current id along the d-axis (direct axis) coinciding with the field pole direction and the phase current iq along the q-axis (quadrature axis) which is orthogonal to the d-axis.
On the other hand, the output power Pg generated by the three-phase synchronous machine in the generator operation mode is given by:
Pg=3{xcfx89xc2x7xcexa8xc2x7iq+i2+xcfx89(Ldxe2x88x92Lq)idxc2x7iq}xe2x80x83xe2x80x83(3)
where xcfx89 represents an electrical angular velocity which corresponds to the rotation speed, and R represents the armature resistance value in each phase. Incidentally, in the expressions mentioned above, the polarities are presumed to be positive in the motor operation mode.
In general, in the case of the synchronous machine of the salient-pole type, it is known that the relation between the synchronous inductances Ld and Lq satisfies the conditions given by the undermentioned expression (4):
Ld greater than Lqxe2x80x83xe2x80x83(4)
Further, in the synchronous machine of the cylindrical-pole type, it is also known that the relation between the synchronous inductances Ld and Lq satisfies the condition given by the following expression (5):
Ld=Lqxe2x80x83xe2x80x83(5)
Furthermore, in the synchronous machine of the embedded-pole type, the magnetic permeability in the d-axis direction (NS-pole direction) encompassing the magnet is smaller than the magnetic permeability in the q-axis direction (i.e., direction orthogonal to the NS-pole direction) encompassing magnetic materials such as iron. Thus, the relation between the synchronous inductances Ld and Lq satisfies the following condition:
Ld less than Lqxe2x80x83xe2x80x83(6)
As can be seen from the expressions (1) and (3) mentioned previously, in the case of the synchronous machines of the salient-pole type and the cylindrical-pole type which satisfy the conditions given by the above-mentioned expressions (4) and (5), respectively, a maximum torque can be produced in the motor operation mode while a maximum output power can be generated in the generator operation mode when the synchronous machine is controlled with the direct-axis current id of zero (id=0) for a same armature current i.
On the other hand, in the case of the synchronous machine of the embedded-pole type satisfying the condition given by the above-mentioned expression (6), a maximum torque can be obtained in the motor operation mode while a maximum output power can be obtained in the generator operation mode when the synchronous machine is controlled with the direct-axis current id of negative polarity (id less than 0). This direct-axis current id of negative polarity will be referred to as the field weakening current.
By contrast, in the case of the claw-pole synchronous machine which belongs to the salient-pole type synchronous machine, the condition given by the expression (4) is satisfied. Consequently, the control is performed with the direct-axis current id of zero (id=0) and no field weakening control is carried out with the armature current.
By the way, the terminal voltage V of the synchronous machine can be determined in dependence on the rotation speed xcfx89, the flux linkage xcexa8 between the flux generated by the field current if and the armature coils, the inductance Ld and the resistance R of the armature and given by the following expression (7).
V={(xcfx89xc2x7xcexa8+xcfx89xc2x7Ldxc2x7id+Rxc2x7iq)2+(xcfx89xc2x7Lqxc2x7iqxe2x88x92Rxc2x7id)2}xe2x80x83xe2x80x83(7)
With the field weakening control with the aid of the armature current mentioned previously, it is intended to mean that the direct-axis current id of the armature is caused to flow in the inverse direction so that the magnetic flux is generated in the opposite direction relative to the counter electromotive force E (=xcfx89xc2x7xcexa8) of the armature with a view to making it possible to regulate or adjust the terminal voltage V given by the above expression (7) under the control with the inverter.
Accordingly, the armature direct-axis current id is caused to flow in such direction as to produce the magnetic flux in the opposite direction relative to the magnetic field generated by the field current if.
Parenthetically, when the phase difference angle between the counter electromotive force E of the armature and the armature current is represented by Ø, the direct-axis current (d-axis current) id and the quadrature-axis current (q-axis current) iq are given by the following expressions (8) and (9), respectively.
id=ixc2x7sin Øxe2x80x83xe2x80x83(8)
iq=ixc2x7cos Øxe2x80x83xe2x80x83(9)
Heretofore, in the inverter control of the armature current i in terms of the direct-axis current component id and the quadrature-axis current component iq, the field weakening control with the armature current i is not performed except for the embedded-pole type permanent-magnet synchronous machine exhibiting the inversed salient-pole characteristic.
Such being the circumstances, in the variable speed control of the claw-pole synchronous machine, only the control with the direct-axis current id of zero (id=0), i.e., the control with the armature current i which is in phase with the counter electromotive force E of the armature, is performed and the field weakening control with the armature current is not carried out.
As is apparent from the above, in the conventional claw-pole synchronous machine control known heretofore, the field weakening control based on the regulation of the phase difference angle Ø of the armature current has not been adopted. Consequently, in order to increase the torque or the output power of the claw-pole synchronous machine, it is required to increase correspondingly the field current or the armature current. This however means that the claw-pole synchronous machine has to be implemented in a large size or scale with the power supply capacity also being increased, giving rise to a problem which remains to be solved.
In the light of the state of the art described above, it is an object of the present invention to solve the problem mentioned above by providing an improved method of controlling a claw-pole synchronous machine which can ensure enhanced controllability of operation of the claw-pole synchronous machine without incurring additional expenditure.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to an aspect of the present invention a method of controlling a claw-pole synchronous machine through a combination of a vector control of an armature voltage and an armature current supplied from an inverter power source in combination with a field current control, wherein when the claw-pole synchronous machine is operated as a generator, the field current control is performed on the basis of a demanded output power and rotation speed of the claw-pole synchronous machine while the field weakening control with the armature current is performed by controlling magnitude of the armature current and a phase difference angle thereof.
In a preferred mode for carrying out the method of controlling the claw-pole synchronous machine which is to be operated as the generator, as mentioned above, a command value map may be previously prepared for storage in which magnitudes of the field current and the armature current of the claw-pole synchronous machine are stored in association with a command value for the phase difference angle of the armature current in correspondence to the demanded output power and rotation speed of the claw-pole synchronous machine, and the magnitudes of the field current so that the armature current caused to flow through the claw-pole synchronous machine and the command value for the phase difference angle of the armature current can be determined by referencing the command value map.
In another preferred mode for carrying out the method mentioned above, the command value for the phase difference angle of the armature current to be stored in the command value map may be set to a value which allows the demanded output power to be generated with a maximum efficiency.
According to another aspect of the present invention, there is provided a method of controlling a claw-pole synchronous machine through a vector control of an armature voltage and an armature current supplied from an inverter power source in combination with a field current control, wherein when the claw-pole synchronous machine is operated as a motor, the field current control is performed on the basis of a demanded torque to be produced and a demanded rotation speed of the claw-pole synchronous machine while realizing a field weakening control with the armature current by controlling magnitude of the armature current and a phase difference angle thereof.
In a preferred mode for carrying out the method of controlling the claw-pole synchronous machine which is to be operated as the electric motor, as mentioned above, a command value map may be previously prepared for storage in which magnitudes of the field current and the armature current of the claw-pole synchronous machine are stored in association with a command value for the phase difference angle of the armature current in correspondence to the demanded torque and rotation speed of the claw-pole synchronous machine so that the magnitudes of the field current and the armature current to be supplied to the claw-pole synchronous machine and the command value for the phase difference angle of the armature current can be determined by referencing the command value map.
In still another preferred mode for carrying out the method mentioned just above, the command value for the phase difference angle of the armature current to be stored in the command value map may be set to a value which allows the demanded torque to be generated with a maximum efficiency.
By virtue of the claw-pole synchronous machine controlling method according to the present invention described above, it is possible to control the claw-pole synchronous machine with enhanced control performance without incurring any appreciable additional expenditure in respect to the structure of the claw-pole synchronous machine and the inverter power supply circuit therefor.